1. Field of the Invention
The present invention relates to a structure for mounting a stereo camera apparatus which takes photograph of an object from different points of view for calculating a three-dimensional distance distribution of the object.
2. Description of the Related Art
Generally, image processing by a so-called stereo method is known as an image-based three-dimensional measuring technique. In this stereo method, an object is photographed from different positions with a stereo camera apparatus which is composed of a pair of cameras, or a main camera and a sub-camera. Then a distance between the stereo camera apparatus and the object is determined from a parallax of the same object using camera parameters based on the principle of triangulation. Camera parameters are, for example, the mounting position, focal length of the stereo camera apparatus and the like.
Specifically, in such image processing using the stereo method, a small region in a reference image photographed by the main camera is superimposed on an area within search area set in a comparative image photographed by the sub-camera while successively shifting the small region pixel by pixel. Then, a position of an area within the search area corresponding to the small region of the reference image is obtained, the corresponding area having image signal coincident with image signal of the small region. Information on the distance to the object is then obtained from a positional difference (parallax) of the same object on the pair of the images, or the reference image and the comparative image, using the principle of triangulation.
The stereo camera apparatus used in the aforementioned image processing is installed such that it is oriented to a front of a vehicle, or in an axis direction of the vehicle. A search area to be set in the comparative image is set in a striplike area as shown in FIG. 2A, which extends from a position substantially corresponding to a small region in the reference image toward the main camera. Therefore, as is apparent from FIGS. 2B and 2C, for a small region located in a specific zone of the outside (right side) of the vehicle in the reference image, it is impossible to allocate a corresponding search area in the comparative image and obtain distance information thereon. For this reason, an area in which a three-dimensional distance distribution is generated by the aforementioned image processing is inclined toward the sub-camera side (left side) with respect to the central axis of the vehicle as shown in FIG. 2D. Consequently, it might be impossible to obtain a three-dimensional distance distribution having a sufficiently large area for an object to be photographed.
On the other hand, to enable detection of an infinite distance corresponding point where the parallax is zero when searching through the comparative image for a corresponding position of a small region in the reference image, it is necessary to set a search margin in a matching search area in the comparative image as shown in FIG. 4. When the reference image is produced using up to extreme ends of camera frame, however, it becomes impossible to provide the search margin.